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tactile_msgs

This package contains generic messages to store almost all types of tactile data to facilitate the developments of tools using/processing this tactile data

Concept

TactileState

The design is based on the successful sensor_msgs/JointState.msg.

Tactile raw data might come from different sensors, on different topics. Hence it is important to have messages that can be easily merged together. The sensor field stores each tactile array coming from one sensor.

The main difference with joint_state is that the different sensors might have different data vectors. For this reason a sensor_msgs/ChannelFloat32.msg message is used per sensor, it contains a name and a data vector.

The name of the sensor publishing the data should be unique, to permit merging, the same way joint_names are unique.

This name is used in the robot_description to define each sensor position and characteristics through a sensor tag and some geometries and property fields.

A tactile_state_publisher similar to the joint_state_publisher can take care of multiple sources and merge them into a single topic /tactile_states.

TactileContact

A TactileContact.msg is a processed and maybe calibrated tactile information about the location, the normal and the wrench of the contact. Usually the raw data array of a tactile sensor will be post-processed to better locate the center of contact by weighted average of neighbour tactile cells. If the sensor is not flat, the normal can also be extrapolated from normals of neighbour cells.

The TactileContact.msg is designed to accommodate a single calibrated cell or a processed weighted average over an array of cells, or any blob location on a larger array.

TactileContacts

TactileContacts.msg contains an array of TactileContact msgs.

Compatibility

The messages of some common tactile sensors have been evaluated to check compatibility with TactileState.

  • The MID Tactile fingertips of University Bielefeld use sr_robot_msgs/UBI0All that are fully compatible
  • The tactile skin/flesh of University Bielefeld uses sr_robot_msgs/MidProxAll that are fully compatible
  • Biotac tactile tip of SyntouchLLC use sr_robot_msgs/BiotacAll that are fully compatible if the naming of the raw data contains a suffix matching the individual sensors of a tip (pac pdc tac tdc hall).
  • Roboskin tactile system (Patent No. I0128764) uses 12 x 16bit raw data array per sensor that are fully compatible
  • The F/T tips of King's College London, installed on the Shadow hand use sr_robot_msgs/ShadowContactStateStamped which are compatible with TactileContacts with a re-encoding of the separate components into the wrench: 
    wrench/torque = Ltorque*normal
wrench/force = Fnormal*normal + tangential_force
  • Most arrays can fit the single vector of the sensor_msgs/ChannelFloat32.msg and have the meaning/ordering described in a robot_description.